Alternating current (AC) is a current which periodically changes amperage and reverses direction, the average amperage of which is zero in a period. Compared with direct current (DC) of which direction does not reverse periodically, alternating current transmits electrical power more efficiently. Consequently, alternating current is the form in which electrical power is delivered to businesses and residences.
Because the electrical power of most electric appliances is supplied by alternating current, if the alternating current cannot be supplied of sufficient quality, most electric appliances cannot work normally and may be damaged. Consequently, how to detect whether the alternating current supplies electrical power normally is a solution to solve the problem.
With reference to Taiwan Pat. No. M450732 which discloses a block diagram of a voltage detector. The voltage detector receives a waveform signal from an external alternating current source and compares an amplitude of the waveform signal of the external alternating current source with an amplitude of the waveform signal of a standby alternating current source. At the same time of the external alternating current source and the standby alternating current source, if the amplitude of the waveform signal of the external alternating current source is less than the amplitude of the waveform signal of the standby alternating current source, the voltage of the external alternating current source is lower and less than the rated voltage value of the standby alternating current source. When this occurs a control unit switches a machine from being connected to the external alternating current source to being connected to the standby alternating current source. Consequently, the machine avoids shutdown due to a sudden drop in the voltage of the external alternating current source.
However, the alternate current detector is coupled to the alternating current itself. In the prior art, the voltage detector must be coupled to the external alternating current source to detect and compare the voltage of the external alternating current source in order to detect if the voltage drops. Consequently, the electrical characteristics of the detected electric appliances could influence and interfere. If the alternate current detector detects multiple electric appliances, each electric appliance needs to couple to an alternate current detector.
Even though these disadvantages of the prior art are known, there have been no acceptable and easy solutions to solve the problem.